Beer of a lager type is produced in Japan, Germany and the other countries. Most yeast, which is used for beer brewing of this type, have flocculation properties at the latter period of the brewing and sedimentation properties at the bottom of a tank, so that it is called bottom fermenting yeast. The sedimentation properties of the yeast are important for the influence against recovery and then filtration of the yeast, and flavor and quality of beer in beer brewing. Further, when the properties of the bottom fermenting yeast are stabilized, the yeast has the advantage that it can be repeatedly used as recovery yeast in the beer production steps. In such cases, it is important to determine flocculating properties of bottom fermenting yeast in screening and selection of new yeast.
As a common method to determine flocculating properties of yeast, there are many methods such as a Burns method (J. Inst. Brew., 43, 31, 1937), a Helm method (Wallerstein Laboratory Communications 16, 315, 1953) and the like. In these methods, after culturing and fermenting yeast, collected yeast is artificially flocculated under an atmosphere that the yeast is easily flocculated and sedimented in the presence of Ca ions. By these methods, the flocculation and sedimentation property is determined.
When flocculation property of yeast is decreased or disappeared in the actual beer production steps, it needs to determine whether collected yeast can be repeatedly used or not. For the determination that the non-flocculation is caused by an irreversible change of yeast itself, namely by a mutation, or by a reversible change of not yeast but environment, it takes about two weeks to obtain the results because such a method to determine flocculating properties should be conducted after culturing and fermenting yeast under certain conditions to evaluate.
Mutation of yeast is not caused in all cells at the same time. It is important to isolate single colonies, study the flocculating properties and know the population of mutants. However, in the method to determine flocculating properties, after conventional culturing and fermentation, it is difficult to treat many strains at a time.
In recent years, DNA sequences of laboratory's yeast (Saccharomyces cerevisiae) were made clear in all chromosomes, the presence of several genes participating in flocculating properties was confirmed (Science 274, 546(1996), Nature 387, 7(1997)). In these genes, FLO1 gene on the chromosome I was studied most, and the gene was isolated and analyzed (Japanese Patent Hyohei-7-509372, Yeast, 9, 1 (1993), Yeast, 10, 211 (1994)). The isolation and analysis of FLO5 gene were also reported that the gene was on a different chromosome from FLO1 gene and has high homologous DNA sequences (Science, 265, 2077 (1994), Curr. Genet., 25, 196 (1994)). The isolation and analysis of FLO8 gene also were reported (Agric. Biol. Chem., 47, 2889 (1983), Mol. Gen. Genet., 251, 707 (1986)).
It was found that bottom fermenting yeast had chromosomes derived from both Saccharomyces cerevisiae and Saccharomyces bayanus. However, it was not successful in determination of the flocculating properties of the bottom fermenting yeast by noticing a gene derived from the both yeast (Yeast, 14, 923 (1998), System. Appl. Microbial. in Press (1999)).
In a method that FLO1 and FLO8 genes of Saccharomyces cerevisiae having flocculating properties were noticed, it was not successful in determination of flocculating properties of beer yeast. Further, it was recently found a part of genes having the flocculating properties of beer yeast. It is reported that, by presence of a part of DNA sequences of the genes, presence of the flocculating properties of the beer yeast type can be determined. It is not reported, however, that decrease and disappearance of the flocculating properties can be determined by genetical change of the yeast (Japanese Patent Laid-open Hei 8-205900).